In recent years, studies and researches on a polymer gel are advanced and the polymer gel is applied to various areas. The polymer gel is mainly classified into two kinds of gels of hydrogel and organogel.
The hydrogel is being used, for example, in a biomedical area. In this area, the hydrogel is used as raw materials of a biocompatible material typified by a contact lens, a wound dressing and a conductive adhesive material for a biomedical electrode for connecting an electrocardiographic meter or a low-frequency therapy equipment with a living body. In the adhesive material for a living body, a try to adopt adhesive materials composed of the hydrogel of a polymer gel type instead of conventional adhesive materials in order to reduce cutaneous irritation is made.
Furthermore, the hydrogel is also used in an industrial area other than a biomedical area. It is studied to use the hydrogel, for example, as raw materials of a special adhesive tape which is used in a semiconductor process step, a cell material, various sensors to utilize a stimulus-responsive property such as a heat-sensitive property, and an adhesive material for a vibration-proofing material or earthquake strengthening to utilize viscoelasticity.
On the other hand, as the organogel, there are a gel formed by including a plasticizer such as aliphatic esters in a matrix of crosslinked polyacryl ester, which is used for a living body or a special adhesive tape, a solid electrolyte gel containing polyol as a skeleton, which is used for a cell material, a gel containing a solvent like alkylene carbonate, a polyurethane gel, and a styrene-ethylene based gel in which paraffin is used as a plasticizer.
In recent years, it is studied to newly use the polymer gel for optical uses. Specifically, it is studied to use the polymer gel as spacers of a PDP, a liquid crystal display and a touch panel.
For example, the PDP includes a panel and an optical filter and a gap is provided between the optical filter and the panel in order to protect the panel. Conventional PDPs have a problem that this gap causes a ghost image phenomenon due to the reflection of incident light from an outside and this phenomenon degrade image quality.
Therefore, a polymer gel, which can impart a vibration-proofing property and a buffering property to the gel and can also control stickiness, receives attention in order to solve this problem. That is, by only bonding the panel to optical filter with the polymer gel, it is possible to bond and fix the panel to the optical filter, and to protect the panel. In addition, by filling the gap with the polymer gel, it becomes possible to control the degradation of image quality.
However, the aforementioned well-known gel has several problems.
For example, since the hydrogel contains a large amount of water, if it contacts an electronic material directly, it has a risk of making a short circuit. Therefore, practical use of the hydrogel in this application is difficult. Further, the hydrogel is stable in use at normal temperature or in the vicinity of a body temperature. However, when the gel is exposed to elevated temperatures, hydrolysis of a resin constituting a matrix is accelerated, and on the other hand, when the gel is exposed to extremely low temperatures, the gel may freeze. Accordingly, there is a fear of the durability of the hydrogel.
On the other hand, the organogel does not have adequate stickiness.
The stickiness can be enhanced by set a crosslinking density of a resin in the organogel at a low level to soften the gel itself. Further, it is necessary to lower the crosslinking density as the organogel becomes thin. Then, the processability of the organogel is deteriorated and the precision of a thickness is deteriorated. It is proposed to reinforce the organogel by use of a member such as a supporter or an intermediate base material in order to supplement the deterioration of the precision. However, when these reinforcing materials are used, transparency of the gel tends to deteriorate. Therefore, usable reinforcing materials are limited to reinforcing materials formed from special materials.
In Japanese Unexamined Patent Publication No. 2004-359808 (Patent Document 1), a transparent adhesive material in gel form for placing between the panel and the optical filter, having a buffering property, is proposed. According to this Publication, as an adhesive material to bond the panel to the optical filter, there is proposed a clear gel adhesive material, wherein    (1) a clear gel of the clear gel adhesive material is formed by swelling a solution in which a three-dimensionally crosslinked polymer contains a plasticizer and inorganic particles,    (2) the clear gel contains a liquid plasticizer having a freezing point of −20° C. or lower in an amount 20 to 70% by weight,    (3) the clear gel contains inorganic particles having a primary average particle diameter of 200 nm or less in an amount 1 to 15% by weight,    (4) a resin (resin before crosslinking) composing the three-dimensionally crosslinked polymer is a resin having a glass transition temperature (Tg) of −20° C. or lower and melt viscosity of 50000 mPa·s or more at 130° C., and    (5) a retention power is 5 mm or less under the conditions of 40° C. and load of 490 mN (50 gf) for 2 hours in a test according to JIS Z 0237. Patent Document 1: Japanese Unexamined Patent Publication No. 2004-359808